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June 26, 1962
J. H. BECK
3,041,056
HEAT TREATING APPARATUS
Filed Oct. 14, 1960
64
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INVENTOR.
4JAC0B HOWARD BECK
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ATTORN EYS
United States Patent 0
3,041,056
1
Patented June 26, 1962
1
2
3,041,056
provide a mu?ie having two temperature zones connected
by a sharp temperature gradient transition zone.
A more speci?c object of the present invention is to
provide a mu?le comprising a ?rst section adapted to be
heated to ‘a ?rst relatively high temperature, a second
section adapted to be heated to a second high temperature
HEAT TREATING APPARATUS
Jacob Howard Beck, 44 Varick Hill Road, Newton, Mass.
Filed Oct. 14, 1960, Ser. No. 62,670
6 Claims. (Cl. 263-37)
The present invention relates to a device for heat proc
essing products and materials such ‘as transistors ‘and
which is substantially lower than said ?rst relatively high
temperature, and a short transition section connecting
said two sections and provided with means for preventing
mu?le construction vadapted to provide high rate initial 10 transfer of heat from one section to the other, whereby
heating.
to provide ‘a sharp temperature gradient between said
diodes and more particularly to a new and improved
‘In the heat treatment of many materials in a con
tinuous or intermittent ?ow system where the materials
are conveyed through ‘a mu?ie by means of a conveyor,
it is essential to precisely control the rate of heating
measured in degrees per minute, the temperature at which
heating is effected and also the length of time during
which each item is subjected to heating at the controlled
temperature so as to insure completion of the heating
treatment process according to predetermined require
ments and to prevent destruction or deterioration of the
materials due to excessive temperature or prolonged heat
ing. It is to be noted that in many cases high rates of
heating are essential to achieve certain properties in the
?nal products. In other cases high rates of heating are
used to attain high rates of production. ‘In the heat treat
ment of materials in a muffle, consideration is also given
to attainment of high rates of production without resort
ing to mu?les of excessive length.
The length of the
mu?le is an important consideration for two reasons. 30
The longer the mu?le, the longer the furnace Iand con
sequently the greater the ?oor space occupied by the
furnace. The other reason is that the longer the mu?le,
the more di?icult it is to support it and to provide proper
control of heating and heat retention throughout its
length. If the length of the mu?ie must be kept short,
the only other way to increase production is to shorten
the heat treating cycle. The obvious way to shorten the
heating cycle is by increasing the temperature of the
furnace. Unfortunately, in many cases this is not per
missible due to the danger of melting or otherwise de
stroying articles to be heated. Nevertheless, it has long
been recognized that in many cases a considerable amount
of time is spent in heating the articles or materials to
the desired elevated heating temperature and that this time
can be cut down by at ?rst exposing thematerials or
‘articles to a temperature considerably in excess of the heat
treating temperature for a period of time just su?icient to
raise the materials to the heat treating temperature, and
thereafter rapidly transferring them to a zone in which
the temperature is at the desired level. Heretofore, this
has not been possible with a muffle due to the difficulty
of providing in the mu?ie two adjacent temperature zones
where one zone is at ‘a relatively high temperature and the
other zone is at a relatively low temperature.
Prior at
tempts to provide this type of zoning have been unsatis
factory for the reason that heat from the relatively high
temperature zone has rapidly transferred to the lower tem
perature zone so as to prevent attainment and preserva
tion of the sharp temperature gradient.
On the other
two sections.
Other objects and many of the attendant advantages of
the present invention will become more readily apparent
as reference is had to the following detailed description
when considered together with the accompanying drawings
wherein:
FIG. 1 is a cross-sectional view of a portion of ‘a muffle
embodying a transition section constructed according to
the present invention, the section being taken ‘along line
1--1 of FIG. 2;
FIG. 2 is a longitudinal section taken along line 2-—2
of FIG. 1;
FIG. 3 is a pro?le of the temperature of (a) the mui?e
sections and (b) the articles moving along within the
muffle; and
FIG. 4 is a fragmentary plan view of a typical conveyor
belt used in mu?les of the type embodying the present
invention.
Referring now to FIGS. 1 and 2, there is shown a por
tion of a muf?e embodying the present invention. The
mu?ie comprises two sections 2 and 4 which are joined
by a novel transition section 6. The two mu?ie sections
2 and 4 may be of identical cross-section or, as in the
illustrated embodiment, they may be of different cross
section. In FIGS. 1 and 2, the mu?ie section 2 is of cylin
drical cross-section and is made of a metal which is re
sistive to relatively high temperatures. The mu?le section
4 is also made of metal which is resistive to relatively
high temperatures; however, it is of a ?ve-sided construc
tion, comprising parallel side walls 10 and 12, a horizon
tal bottom wall 14, and two inclined top walls 16 and 18.
Disposed within the cylindrical section 2 is a quartz or
metal plate 20. This plate is located below the axis of
the cylindrical section 2. It extends into the transition
section 6. The purpose of this section 20 is to provide
support to a moving belt conveyor 22 and also to act
as a baf?e to channe1 gases along the cylindrical section
2. The conveyor 22 may be made of a siutable ?exible,
heat-resistant material. Generally, it is made of a wire
mesh. However, it may also‘ be made of ?exible high
temperature metal alloy. The latter form of construction
is illustrated in FIG. 4. In FIG. 4, a flexible metal belt
22a is provided with a plurality of holes 24 which are
sized to receive suitable objects, as, for example, the bases
of transistors or diodes or other semiconductors. The ob
jects to be treated are placed on the belt, one to a hole,
and are then transported through the mu?le by the belt
so as to be subjected to a controlled heat treatment. It is
to be understood that the objects need not be transported
through the mu?le by a conveyor belt. Instead they may
mote zone having the desired temperature is unsatisfactory
be conveyed through the furnace by means of a pusher.
since there is a tendency for liquid metal to splash or to
As seen in FIG. 2, the cylindrical muf?e section 2 is
deform, resulting in inferior products.
surrounded by the turns ‘of an electric heating coil 30.
Accordingly, it is the primary object of the present in 65 The second muffle section 4 also is surrounded by the turns
vent-ion to provide a muffle construction comprising two
of a second electric heating coil 32. These coils are
successive and adjacent temperature zones for heat treat
representative of the type of heating elements which may
ment, one temperature zone featuring a relatively high
be used in association with the mu?ie. Alternatively, the
temperature and the other temperature zone having a
mu?le may be heated by other types of electric heaters
relatively low temperature, whereby to provide a sharp 70 and, in certain special cases, may also be heated by other
temperature gradient between the two zones.
types of electric heaters and, in certain special cases, may
A more speci?c object of the present invention is to ' also be heated by gas heaters. In the illustrated embodi
hand, rapid transfer of the materials or articles to a re
3,041,056
4
ment, it is to be understood that the electric heater 30
is designed to raise the muf?e 2 to a temperature consid
erably in excess of the temperature to which the second
mu?le section 4 is raised by the heater 32. In a typical in
stallation, the mu?le section 2 is raised to a temperature
ty degree difference in temperature being required to olf
set heat losses due to radiation-,conduction, and ‘absorp
tion by gasses which may be within the muffle.
Under the foregoing conditions, there will be a sharp
temperature gradient in the region of transition section 6.
Curve A of FIG. 3 presents a'pr’o?le of the temperature
of approximately 1200” C. while the second mu?le sec
tion 4 is adapted to be heated to a temperature of approx
in the mu?ie. Proceeding from left to right, the ?rst hori
imately 600° C. Because of this di?erence of tempera
zontal portion of curve A represents the temperature in
ture, there is a great tendency for the heat in the muffle
zone I which is 1200° C. The second horizontal por
section 2 to be transferred to the second mu?le section 4. 10 tion represents the temperature in zone II which is
However, this is effectively prevented by the transition sec
620° C. The intermediate portion of curve A represents
tion 6 which produces and maintains a sharp temperature
the sharp drop or gradient in temperature which occurs
gradient between the two mu?ie sections.
at the transition section 6. Curve B of FIG. 3 is a pro
The transition section 6 comprises two cylindrical
?le of the temperature of an article passing through the
plates 38 and 40, the former being welded to the cylin 15 muffle on conveyor belt 22. By suitable adjustment of
drical mu?le section 2 and the latter being welded to the
the speed of the conveyor belt 22, the articles on the"
polygonal muf?e section 4. At its center, the circular
conveyor belt can be made to have a temperature of
plate 38 is provided with an opening 42 which matches
approximately 600° C. as they pass from zone I. Be
the interior configuration of muffle section 2. The other
cause of the high temperature of the cylindrical mu?le
circular plate 40 is provided with a central opening 44
section 2, the time required to heat each article to 600° C.
which similarly corresponds in shape to the interior open
will be relatively brief, as indicated by the slope of the
ing of the polygonal muf?e section 4. The two plates are
inclined portion of curve B. Once in mu?le section II,
welded to the two mu?ie sections as indicated at 48 and
the articles will exhibit a constant temperature of 600° C.,
50.
as indicated by the horizontal portion of curve B.
The two plates 38 and 40 are spaced from each other 25 That such a sharp temperature gradient can be ob
by a circular ring of pipe 52 which is interposed between
tained is due entirely to the construction of section 6.
them. The circular ring of pipe 52 is welded as at 54 to
First of all, the amount of heat which can be transferred
the peripheral edges of the two plates 38 and 40, with ap
by convection is negligible due to the fact that the hydro
proximately half of the exterior surface of the pipe 52
gen gas has a low speci?c heat and the amount of gas is
being exposed to the space enclosed between the two 30 relatively small. Secondly, little or no heat is trans
plates 38 and 40. From the foregoing description it will
ferred from the cylindrical muffle section 2 to the polygo
be appreciated that the two plates 38 and 40 cooperate
nal mu?ie section 4 by conduction. The loop provided
with the pipe 52 to de?ne a chamber 56. As illustrated
by the pipe 52 completely prevents transfer of heat by
in FIG. 1, the ends of the pipe 52 are butt welded tlol'a
conduction. The cold water circulating in the pipe 52
circular disc 58 so as to form an elongated split ring 35 will substantially absorb most of the heat which would
chamber 60. Welded to one end and communicating with
tend to pass by conduction from the mu?le section 2' to
chamber 69 is an inlet pipe 62. Welded to the opposite
muf?e section 4 through plate 38, pipe 52, and plate 40.
end of pipe 52 and also communicating with chamber
Transfer of heat by radiation is also substantially elimi
60 is an outlet pipe 64. The inlet pipe 62 and the outlet
nated by the virtue of the radiation shield 68. Any heat
pipe 64 are connected to a cold water source and circu
40
which is radiated by plate 38 toward the opposite plate
40 will be intercepted by the radiation shield 68. The
heat picked up by shield 68 from plate 38 will be trans
plates 38 and 40 is a circular metal plate 68 which is
ferred to pipe 52 by conduction, where-at it will be ab
provided at its center withran opening 70 which is just
sorbed ‘by the circulating water and removed from the
large enough to accommodate the conveyor belt 22 and 45 system.
also to permit passage therethrough of articles which ‘are
Obviously, the greater the temperature difference be
suported on the traveling conveyor belt. Although only
tween the two mu?le sections the more advantageous it
lating unit which is schematically represented at 66.
Welded to the pipe 52 and interposed between the two
one metal plate 68 is shown, it is to be understood that
more than one plate may be welded to the pipe 52 between
the two plates 38 and 40. As explained hereinafter, the
is to use more than one radiation shield. It is also be
lieved to be apparent that the amount of heat which can
be removed per unit time can be increased without de
plate 68 functions as a radiation shield.
creasing the temperature of the water fed to pipe 52 and
The operation of 'the transition section 6 will now be
without increasing the volume of water which is pumped
described, with reference had to FIG. 3 to facilitate expla
through pipe 52. This can be accomplished by adding
nation;
additional pipe so that there are a plurality of turns in
‘Assume for purposes of discussion that the conveyor 55 stead of a single turn of pipe. The pipe could be bent in
belt 22 carries semiconductor units which are to be heat
the form of a helix, in which case water would be fed
treated to a temperature of'approximately 600° C. In
into one end' of the helix and removed from the other.
the‘ alloying or brazing of semi-conductors such as transis
The sole requirement is that the turns of the pipe helix
tors, it is customary to provide a hydrogen atmosphere
be welded to each other and also to the plates 38 and 40
muffle. Accordingly, with respect to the situation under 60 so as to provide adequate support for the two muffle
discussion, let it also be assumed that hydrogen is ?owing
from the cylindrical mu?le section 2 into the polygonal
sections.
'
.
.
It is to be noted that the present invention provides
7 mu?lersection 4. through the transition section 6. Assume
obtainment of a sharp temperature gradient by means
also that because of certain physical characteristics of
of structure which is relatively inexpensive and easy to
the semi-conductors, they should not be heated to a tem 65 fabricate ‘and which does not necessitate peculiar or
perature above 700° ‘C. Assume further that the semi
special cross-sectional con?gurations for the muf?e. On
conductors when inserted into the mu?le furnace are at
the ‘other hand, the invention is not limited to mu?ies
room temperature and that it is desired to elevate them
having circular and pentagonal cross-sectional con?gura
' to the treating temperature of 600° C. within a short time
tions. The cross-sectional con?gurations of the muf?e are
such as thirty seconds. In such a situation, the cylindrij 70 irrelevant so far as the transition section is concerned.
cal muf?e section 2 (Zone I) would be heated by the elec
However, it is appreciated that other factors may neces
tric heater 30 to a suitably high temperature, as, for
sitate a particular cross-sectional muffle con?guration.
example, 1200° C. The second muf?e section 4 (zone II)
The transition section 6 does not limit the construction
would be heated, to'a temperature slightly higher than '
or operation of the conveyor; nor does it affect the ex
600° C. as, for example, apprxoimately 620° C., the twen 75 terior construction of the furnace. The piping required
5
3,041,056
to furnish water to the transition section 6 is no more
elaborate or di?icult to provide than is the piping for
jackets for heating and cooling heretofore employed in
muffle-type furnaces. A further important advantage of
the present invention is that the various elements of the
muffle may be made of the same type of material,
6
for preventing transfer of heat by conduction and radia
tion between said two plates.
2. A muf?e construction comprising a ?rst mu?le sec
tion connected in series with a second muf?e section by
means of a third transition mu?le section, said transi
tion mu?ie section comprising two parallel plates pro
thereby avoiding problems of bonding and danger of rup
vided with central openings, one of said plates being se
ture due to different coe?icients of expansion. In prac
cured adjacent its central opening to said ?rst muf?e
tice, it is preferred that the plates 38‘, 40, and 68, to
section and the other of said plates being secured ad
gether with pipe 52, be made of high-temperature stain 10 jacent its central opening to the second mu?le section,
less steel which can be welded without dif?culty. For the
means for heating said ?rst muffle section to a ?rst rela
same reason, it is also preferred that the mu?le sections
tively high temperature T1, means for heating said sec
2 and 4 be made of high-temperature stainless steel.
ond mu?le section to a second relatively low tempera
These materials are particularly resistant to the types
ture T2, ?rst means interposed between said two plates
of gaseous atmospheres which are conventionally em 15 and secured thereto for preventing transfer of heat by
ployed in mulfle-type furnaces. It is to be observed, also,
conduction between said two plates, and second means
that the construction of the transition section in no way
connected to said ?rst means for preventing transfer of
limits the type of heaters which may be employed with
heat from said one plate to said other plate by radiation.
the two mu?le sections. If desired, ?at heaters may be
3. A muf?e as de?ned by claim 2 wherein said means
used in place of heaters 30 and 32. A further advan 20 for preventing heat transfer by conduction is a pipe se
tage of the construction of the transition section is that
cured to said plates at their periphery and totally enclos
it does not occupy much space. In this connection, it
ing the space between said two plates, said pipe having
is to be observed that in a furnace it is the general pro
inlet and outlet openings whereby cooling ?uid may be
cedure to place insulation about the mu?le so as to avoid
supplied to and removed from said pipe for the purpose
transfer of heat from the muffle to the outside casing of 25 of removing heat from said transition section.
the furnace. The insulation is generally in the form of
4. A muf?e as de?ned by claim 2 wherein said means
blocks or slabs which are laid up along the outside of
for preventing heat transfer by radiation is a third plate
the muffle. The illustrated construction for the transi
interposed between said two plates and secured to said
tion section presents no problems with respect to place
means for preventing heat transfer by radiation.
ment or type of insulating material.
30
5. A ‘mu?ie including a transition section adapted to
Other advantages of the present invention will be obvi
provide and preserve a sharp temperature gradiant be
ous to persons skilled in the art. Similarly, it will be
tween ?rst and second points in said muffle, said transition
obvious to persons skilled in the art that the instant in
section comprising two plates in parallel-spaced relation
vention is susceptible to many changes and variations
with each other, and a pipe secured to said plates at their
without departing from the principles outlined above. 35 periphery, said pipe totally enclosing the space between
Accordingly, this invention is not to be limited except by
said two plates, said pipe having a ?rst inlet opening and
the following claims.
a second outlet opening whereby ?uid may be supplied
I claim:
to and removed from said pipe for the purpose of remov
1. A muffle comprising a ?rst muf?e section connected
ing heat from said transition section, and a radiation
in series with a second mu?le section by means of a
shield disposed between said two plates and secured to
third relatively short transition muf?e section having a
said pipe.
larger cross section than said ?rst and second muffle sec
6. A muf?e as de?ned by claim 5 wherein said radia
tions, the three mu?le sections de?ning a continuous un
tion shield has a central opening in registration with the
obstructed passageway to accommodate a continuous
interior of said mnf?e, whereby to permit objects to be
conveyor for transporting articles to be heat treated in 45 transferred between said two points in said muffle through
the muf?e, said third transition muffle section compris
said transition section.
ing two parallel plates provided with central openings
with one of said plates secured adjacent its central open
ing to said ?rst mui?e section and the other of said
plates secured adjacent its central opening to the second 50
mu?le section, means for heating said ?rst muffle sec
tion to a ?rst temperature T1, means for heating said
second mu?le section to a second temperature T2, and
1,795,819
Axell _______________ __ Mar. 10, 1931
2,086,672
2,269,645
Heyman ____________ __ July 13, 1937
Browning ____________ __ Ian. 13, 1942.
means permanently interposed between said two plates
2,839,284
Gilbert ______________ __ June 17, 1958
References Cited in the ?le of this patent
UNITED STATES PATENTS